/*-*************************************
 *  Dependencies
 ***************************************/
#include <stdio.h>  /* fprintf */
#include <stdlib.h> /* malloc, free, qsort */
#include <string.h> /* memset */
#include <time.h>   /* clock */

#include "cover.h"
#include "mem.h" /* read */
#include "pool.h"
#include "threading.h"
#include "zstd_internal.h" /* includes zstd.h */
#ifndef ZDICT_STATIC_LINKING_ONLY
#define ZDICT_STATIC_LINKING_ONLY
#endif
#include "zdict.h"

/*-*************************************
 *  Constants
 ***************************************/
#define FASTCOVER_MAX_SAMPLES_SIZE (sizeof(size_t) == 8 ? ((unsigned)-1) : ((unsigned)1 GB))
#define FASTCOVER_MAX_F 31
#define FASTCOVER_MAX_ACCEL 10
#define DEFAULT_SPLITPOINT 0.75
#define DEFAULT_F 20
#define DEFAULT_ACCEL 1

/*-*************************************
 *  Console display
 ***************************************/
static int g_displayLevel = 2;
#define DISPLAY(...)                  \
    {                                 \
        fprintf(stderr, __VA_ARGS__); \
        fflush(stderr);               \
    }
#define LOCALDISPLAYLEVEL(displayLevel, l, ...) \
    if (displayLevel >= l) {                    \
        DISPLAY(__VA_ARGS__);                   \
    } /* 0 : no display;   1: errors;   2: default;  3: details;  4: debug */
#define DISPLAYLEVEL(l, ...) LOCALDISPLAYLEVEL(g_displayLevel, l, __VA_ARGS__)

#define LOCALDISPLAYUPDATE(displayLevel, l, ...)                       \
    if (displayLevel >= l) {                                           \
        if ((clock() - g_time > refreshRate) || (displayLevel >= 4)) { \
            g_time = clock();                                          \
            DISPLAY(__VA_ARGS__);                                      \
        }                                                              \
    }
#define DISPLAYUPDATE(l, ...) LOCALDISPLAYUPDATE(g_displayLevel, l, __VA_ARGS__)
static const clock_t refreshRate = CLOCKS_PER_SEC * 15 / 100;
static clock_t g_time = 0;

/*-*************************************
 * Hash Functions
 ***************************************/
static const U64 prime6bytes = 227718039650203ULL;
static size_t ZSTD_hash6(U64 u, U32 h) {
    return (size_t)(((u << (64 - 48)) * prime6bytes) >> (64 - h));
}
static size_t ZSTD_hash6Ptr(const void* p, U32 h) {
    return ZSTD_hash6(MEM_readLE64(p), h);
}

static const U64 prime8bytes = 0xCF1BBCDCB7A56463ULL;
static size_t ZSTD_hash8(U64 u, U32 h) {
    return (size_t)(((u)*prime8bytes) >> (64 - h));
}
static size_t ZSTD_hash8Ptr(const void* p, U32 h) {
    return ZSTD_hash8(MEM_readLE64(p), h);
}

/**
 * Hash the d-byte value pointed to by p and mod 2^f
 */
static size_t FASTCOVER_hashPtrToIndex(const void* p, U32 h, unsigned d) {
    if (d == 6) {
        return ZSTD_hash6Ptr(p, h) & ((1 << h) - 1);
    }
    return ZSTD_hash8Ptr(p, h) & ((1 << h) - 1);
}

/*-*************************************
 * Acceleration
 ***************************************/
typedef struct {
    unsigned finalize; /* Percentage of training samples used for ZDICT_finalizeDictionary */
    unsigned skip;     /* Number of dmer skipped between each dmer counted in computeFrequency */
} FASTCOVER_accel_t;

static const FASTCOVER_accel_t FASTCOVER_defaultAccelParameters[FASTCOVER_MAX_ACCEL + 1] = {
    {100, 0}, /* accel = 0, should not happen because accel = 0 defaults to accel = 1 */
    {100, 0}, /* accel = 1 */
    {50, 1},  /* accel = 2 */
    {34, 2},  /* accel = 3 */
    {25, 3},  /* accel = 4 */
    {20, 4},  /* accel = 5 */
    {17, 5},  /* accel = 6 */
    {14, 6},  /* accel = 7 */
    {13, 7},  /* accel = 8 */
    {11, 8},  /* accel = 9 */
    {10, 9},  /* accel = 10 */
};

/*-*************************************
 * Context
 ***************************************/
typedef struct {
    const BYTE* samples;
    size_t* offsets;
    const size_t* samplesSizes;
    size_t nbSamples;
    size_t nbTrainSamples;
    size_t nbTestSamples;
    size_t nbDmers;
    U32* freqs;
    unsigned d;
    unsigned f;
    FASTCOVER_accel_t accelParams;
} FASTCOVER_ctx_t;

/*-*************************************
 *  Helper functions
 ***************************************/
/**
 * Selects the best segment in an epoch.
 * Segments of are scored according to the function:
 *
 * Let F(d) be the frequency of all dmers with hash value d.
 * Let S_i be hash value of the dmer at position i of segment S which has length k.
 *
 *     Score(S) = F(S_1) + F(S_2) + ... + F(S_{k-d+1})
 *
 * Once the dmer with hash value d is in the dictionary we set F(d) = 0.
 */
static COVER_segment_t FASTCOVER_selectSegment(const FASTCOVER_ctx_t* ctx,
                                               U32* freqs,
                                               U32 begin,
                                               U32 end,
                                               ZDICT_cover_params_t parameters,
                                               U16* segmentFreqs) {
    /* Constants */
    const U32 k = parameters.k;
    const U32 d = parameters.d;
    const U32 f = ctx->f;
    const U32 dmersInK = k - d + 1;

    /* Try each segment (activeSegment) and save the best (bestSegment) */
    COVER_segment_t bestSegment = {0, 0, 0};
    COVER_segment_t activeSegment;

    /* Reset the activeDmers in the segment */
    /* The activeSegment starts at the beginning of the epoch. */
    activeSegment.begin = begin;
    activeSegment.end = begin;
    activeSegment.score = 0;

    /* Slide the activeSegment through the whole epoch.
     * Save the best segment in bestSegment.
     */
    while (activeSegment.end < end) {
        /* Get hash value of current dmer */
        const size_t idx = FASTCOVER_hashPtrToIndex(ctx->samples + activeSegment.end, f, d);

        /* Add frequency of this index to score if this is the first occurrence of index in active segment */
        if (segmentFreqs[idx] == 0) {
            activeSegment.score += freqs[idx];
        }
        /* Increment end of segment and segmentFreqs*/
        activeSegment.end += 1;
        segmentFreqs[idx] += 1;
        /* If the window is now too large, drop the first position */
        if (activeSegment.end - activeSegment.begin == dmersInK + 1) {
            /* Get hash value of the dmer to be eliminated from active segment */
            const size_t delIndex = FASTCOVER_hashPtrToIndex(ctx->samples + activeSegment.begin, f, d);
            segmentFreqs[delIndex] -= 1;
            /* Subtract frequency of this index from score if this is the last occurrence of this index in active
             * segment */
            if (segmentFreqs[delIndex] == 0) {
                activeSegment.score -= freqs[delIndex];
            }
            /* Increment start of segment */
            activeSegment.begin += 1;
        }

        /* If this segment is the best so far save it */
        if (activeSegment.score > bestSegment.score) {
            bestSegment = activeSegment;
        }
    }

    /* Zero out rest of segmentFreqs array */
    while (activeSegment.begin < end) {
        const size_t delIndex = FASTCOVER_hashPtrToIndex(ctx->samples + activeSegment.begin, f, d);
        segmentFreqs[delIndex] -= 1;
        activeSegment.begin += 1;
    }

    {
        /*  Zero the frequency of hash value of each dmer covered by the chosen segment. */
        U32 pos;
        for (pos = bestSegment.begin; pos != bestSegment.end; ++pos) {
            const size_t i = FASTCOVER_hashPtrToIndex(ctx->samples + pos, f, d);
            freqs[i] = 0;
        }
    }

    return bestSegment;
}

static int FASTCOVER_checkParameters(ZDICT_cover_params_t parameters, size_t maxDictSize, unsigned f, unsigned accel) {
    /* k, d, and f are required parameters */
    if (parameters.d == 0 || parameters.k == 0) {
        return 0;
    }
    /* d has to be 6 or 8 */
    if (parameters.d != 6 && parameters.d != 8) {
        return 0;
    }
    /* k <= maxDictSize */
    if (parameters.k > maxDictSize) {
        return 0;
    }
    /* d <= k */
    if (parameters.d > parameters.k) {
        return 0;
    }
    /* 0 < f <= FASTCOVER_MAX_F*/
    if (f > FASTCOVER_MAX_F || f == 0) {
        return 0;
    }
    /* 0 < splitPoint <= 1 */
    if (parameters.splitPoint <= 0 || parameters.splitPoint > 1) {
        return 0;
    }
    /* 0 < accel <= 10 */
    if (accel > 10 || accel == 0) {
        return 0;
    }
    return 1;
}

/**
 * Clean up a context initialized with `FASTCOVER_ctx_init()`.
 */
static void FASTCOVER_ctx_destroy(FASTCOVER_ctx_t* ctx) {
    if (!ctx)
        return;

    free(ctx->freqs);
    ctx->freqs = NULL;

    free(ctx->offsets);
    ctx->offsets = NULL;
}

/**
 * Calculate for frequency of hash value of each dmer in ctx->samples
 */
static void FASTCOVER_computeFrequency(U32* freqs, const FASTCOVER_ctx_t* ctx) {
    const unsigned f = ctx->f;
    const unsigned d = ctx->d;
    const unsigned skip = ctx->accelParams.skip;
    const unsigned readLength = MAX(d, 8);
    size_t i;
    assert(ctx->nbTrainSamples >= 5);
    assert(ctx->nbTrainSamples <= ctx->nbSamples);
    for (i = 0; i < ctx->nbTrainSamples; i++) {
        size_t start = ctx->offsets[i]; /* start of current dmer */
        size_t const currSampleEnd = ctx->offsets[i + 1];
        while (start + readLength <= currSampleEnd) {
            const size_t dmerIndex = FASTCOVER_hashPtrToIndex(ctx->samples + start, f, d);
            freqs[dmerIndex]++;
            start = start + skip + 1;
        }
    }
}

/**
 * Prepare a context for dictionary building.
 * The context is only dependent on the parameter `d` and can used multiple
 * times.
 * Returns 0 on success or error code on error.
 * The context must be destroyed with `FASTCOVER_ctx_destroy()`.
 */
static size_t FASTCOVER_ctx_init(FASTCOVER_ctx_t* ctx,
                                 const void* samplesBuffer,
                                 const size_t* samplesSizes,
                                 unsigned nbSamples,
                                 unsigned d,
                                 double splitPoint,
                                 unsigned f,
                                 FASTCOVER_accel_t accelParams) {
    const BYTE* const samples = (const BYTE*)samplesBuffer;
    const size_t totalSamplesSize = COVER_sum(samplesSizes, nbSamples);
    /* Split samples into testing and training sets */
    const unsigned nbTrainSamples = splitPoint < 1.0 ? (unsigned)((double)nbSamples * splitPoint) : nbSamples;
    const unsigned nbTestSamples = splitPoint < 1.0 ? nbSamples - nbTrainSamples : nbSamples;
    const size_t trainingSamplesSize = splitPoint < 1.0 ? COVER_sum(samplesSizes, nbTrainSamples) : totalSamplesSize;
    const size_t testSamplesSize =
        splitPoint < 1.0 ? COVER_sum(samplesSizes + nbTrainSamples, nbTestSamples) : totalSamplesSize;

    /* Checks */
    if (totalSamplesSize < MAX(d, sizeof(U64)) || totalSamplesSize >= (size_t)FASTCOVER_MAX_SAMPLES_SIZE) {
        DISPLAYLEVEL(1,
                     "Total samples size is too large (%u MB), maximum size is %u MB\n",
                     (unsigned)(totalSamplesSize >> 20),
                     (FASTCOVER_MAX_SAMPLES_SIZE >> 20));
        return ERROR(srcSize_wrong);
    }

    /* Check if there are at least 5 training samples */
    if (nbTrainSamples < 5) {
        DISPLAYLEVEL(1, "Total number of training samples is %u and is invalid\n", nbTrainSamples);
        return ERROR(srcSize_wrong);
    }

    /* Check if there's testing sample */
    if (nbTestSamples < 1) {
        DISPLAYLEVEL(1, "Total number of testing samples is %u and is invalid.\n", nbTestSamples);
        return ERROR(srcSize_wrong);
    }

    /* Zero the context */
    memset(ctx, 0, sizeof(*ctx));
    DISPLAYLEVEL(2, "Training on %u samples of total size %u\n", nbTrainSamples, (unsigned)trainingSamplesSize);
    DISPLAYLEVEL(2, "Testing on %u samples of total size %u\n", nbTestSamples, (unsigned)testSamplesSize);

    ctx->samples = samples;
    ctx->samplesSizes = samplesSizes;
    ctx->nbSamples = nbSamples;
    ctx->nbTrainSamples = nbTrainSamples;
    ctx->nbTestSamples = nbTestSamples;
    ctx->nbDmers = trainingSamplesSize - MAX(d, sizeof(U64)) + 1;
    ctx->d = d;
    ctx->f = f;
    ctx->accelParams = accelParams;

    /* The offsets of each file */
    ctx->offsets = (size_t*)calloc((nbSamples + 1), sizeof(size_t));
    if (ctx->offsets == NULL) {
        DISPLAYLEVEL(1, "Failed to allocate scratch buffers \n");
        FASTCOVER_ctx_destroy(ctx);
        return ERROR(memory_allocation);
    }

    /* Fill offsets from the samplesSizes */
    {
        U32 i;
        ctx->offsets[0] = 0;
        assert(nbSamples >= 5);
        for (i = 1; i <= nbSamples; ++i) {
            ctx->offsets[i] = ctx->offsets[i - 1] + samplesSizes[i - 1];
        }
    }

    /* Initialize frequency array of size 2^f */
    ctx->freqs = (U32*)calloc(((U64)1 << f), sizeof(U32));
    if (ctx->freqs == NULL) {
        DISPLAYLEVEL(1, "Failed to allocate frequency table \n");
        FASTCOVER_ctx_destroy(ctx);
        return ERROR(memory_allocation);
    }

    DISPLAYLEVEL(2, "Computing frequencies\n");
    FASTCOVER_computeFrequency(ctx->freqs, ctx);

    return 0;
}

/**
 * Given the prepared context build the dictionary.
 */
static size_t FASTCOVER_buildDictionary(const FASTCOVER_ctx_t* ctx,
                                        U32* freqs,
                                        void* dictBuffer,
                                        size_t dictBufferCapacity,
                                        ZDICT_cover_params_t parameters,
                                        U16* segmentFreqs) {
    BYTE* const dict = (BYTE*)dictBuffer;
    size_t tail = dictBufferCapacity;
    /* Divide the data into epochs. We will select one segment from each epoch. */
    const COVER_epoch_info_t epochs = COVER_computeEpochs((U32)dictBufferCapacity, (U32)ctx->nbDmers, parameters.k, 1);
    const size_t maxZeroScoreRun = 10;
    size_t zeroScoreRun = 0;
    size_t epoch;
    DISPLAYLEVEL(2, "Breaking content into %u epochs of size %u\n", (U32)epochs.num, (U32)epochs.size);
    /* Loop through the epochs until there are no more segments or the dictionary
     * is full.
     */
    for (epoch = 0; tail > 0; epoch = (epoch + 1) % epochs.num) {
        const U32 epochBegin = (U32)(epoch * epochs.size);
        const U32 epochEnd = epochBegin + epochs.size;
        size_t segmentSize;
        /* Select a segment */
        COVER_segment_t segment = FASTCOVER_selectSegment(ctx, freqs, epochBegin, epochEnd, parameters, segmentFreqs);

        /* If the segment covers no dmers, then we are out of content.
         * There may be new content in other epochs, for continue for some time.
         */
        if (segment.score == 0) {
            if (++zeroScoreRun >= maxZeroScoreRun) {
                break;
            }
            continue;
        }
        zeroScoreRun = 0;

        /* Trim the segment if necessary and if it is too small then we are done */
        segmentSize = MIN(segment.end - segment.begin + parameters.d - 1, tail);
        if (segmentSize < parameters.d) {
            break;
        }

        /* We fill the dictionary from the back to allow the best segments to be
         * referenced with the smallest offsets.
         */
        tail -= segmentSize;
        memcpy(dict + tail, ctx->samples + segment.begin, segmentSize);
        DISPLAYUPDATE(2, "\r%u%%       ", (unsigned)(((dictBufferCapacity - tail) * 100) / dictBufferCapacity));
    }
    DISPLAYLEVEL(2, "\r%79s\r", "");
    return tail;
}

/**
 * Parameters for FASTCOVER_tryParameters().
 */
typedef struct FASTCOVER_tryParameters_data_s {
    const FASTCOVER_ctx_t* ctx;
    COVER_best_t* best;
    size_t dictBufferCapacity;
    ZDICT_cover_params_t parameters;
} FASTCOVER_tryParameters_data_t;

/**
 * Tries a set of parameters and updates the COVER_best_t with the results.
 * This function is thread safe if zstd is compiled with multithreaded support.
 * It takes its parameters as an *OWNING* opaque pointer to support threading.
 */
static void FASTCOVER_tryParameters(void* opaque) {
    /* Save parameters as local variables */
    FASTCOVER_tryParameters_data_t* const data = (FASTCOVER_tryParameters_data_t*)opaque;
    const FASTCOVER_ctx_t* const ctx = data->ctx;
    const ZDICT_cover_params_t parameters = data->parameters;
    size_t dictBufferCapacity = data->dictBufferCapacity;
    size_t totalCompressedSize = ERROR(GENERIC);
    /* Initialize array to keep track of frequency of dmer within activeSegment */
    U16* segmentFreqs = (U16*)calloc(((U64)1 << ctx->f), sizeof(U16));
    /* Allocate space for hash table, dict, and freqs */
    BYTE* const dict = (BYTE* const)malloc(dictBufferCapacity);
    COVER_dictSelection_t selection = COVER_dictSelectionError(ERROR(GENERIC));
    U32* freqs = (U32*)malloc(((U64)1 << ctx->f) * sizeof(U32));
    if (!segmentFreqs || !dict || !freqs) {
        DISPLAYLEVEL(1, "Failed to allocate buffers: out of memory\n");
        goto _cleanup;
    }
    /* Copy the frequencies because we need to modify them */
    memcpy(freqs, ctx->freqs, ((U64)1 << ctx->f) * sizeof(U32));
    /* Build the dictionary */
    {
        const size_t tail = FASTCOVER_buildDictionary(ctx, freqs, dict, dictBufferCapacity, parameters, segmentFreqs);

        const unsigned nbFinalizeSamples = (unsigned)(ctx->nbTrainSamples * ctx->accelParams.finalize / 100);
        selection = COVER_selectDict(dict + tail,
                                     dictBufferCapacity - tail,
                                     ctx->samples,
                                     ctx->samplesSizes,
                                     nbFinalizeSamples,
                                     ctx->nbTrainSamples,
                                     ctx->nbSamples,
                                     parameters,
                                     ctx->offsets,
                                     totalCompressedSize);

        if (COVER_dictSelectionIsError(selection)) {
            DISPLAYLEVEL(1, "Failed to select dictionary\n");
            goto _cleanup;
        }
    }
_cleanup:
    free(dict);
    COVER_best_finish(data->best, parameters, selection);
    free(data);
    free(segmentFreqs);
    COVER_dictSelectionFree(selection);
    free(freqs);
}

static void FASTCOVER_convertToCoverParams(ZDICT_fastCover_params_t fastCoverParams,
                                           ZDICT_cover_params_t* coverParams) {
    coverParams->k = fastCoverParams.k;
    coverParams->d = fastCoverParams.d;
    coverParams->steps = fastCoverParams.steps;
    coverParams->nbThreads = fastCoverParams.nbThreads;
    coverParams->splitPoint = fastCoverParams.splitPoint;
    coverParams->zParams = fastCoverParams.zParams;
    coverParams->shrinkDict = fastCoverParams.shrinkDict;
}

static void FASTCOVER_convertToFastCoverParams(ZDICT_cover_params_t coverParams,
                                               ZDICT_fastCover_params_t* fastCoverParams,
                                               unsigned f,
                                               unsigned accel) {
    fastCoverParams->k = coverParams.k;
    fastCoverParams->d = coverParams.d;
    fastCoverParams->steps = coverParams.steps;
    fastCoverParams->nbThreads = coverParams.nbThreads;
    fastCoverParams->splitPoint = coverParams.splitPoint;
    fastCoverParams->f = f;
    fastCoverParams->accel = accel;
    fastCoverParams->zParams = coverParams.zParams;
    fastCoverParams->shrinkDict = coverParams.shrinkDict;
}

ZDICTLIB_API size_t ZDICT_trainFromBuffer_fastCover(void* dictBuffer,
                                                    size_t dictBufferCapacity,
                                                    const void* samplesBuffer,
                                                    const size_t* samplesSizes,
                                                    unsigned nbSamples,
                                                    ZDICT_fastCover_params_t parameters) {
    BYTE* const dict = (BYTE*)dictBuffer;
    FASTCOVER_ctx_t ctx;
    ZDICT_cover_params_t coverParams;
    FASTCOVER_accel_t accelParams;
    /* Initialize global data */
    g_displayLevel = parameters.zParams.notificationLevel;
    /* Assign splitPoint and f if not provided */
    parameters.splitPoint = 1.0;
    parameters.f = parameters.f == 0 ? DEFAULT_F : parameters.f;
    parameters.accel = parameters.accel == 0 ? DEFAULT_ACCEL : parameters.accel;
    /* Convert to cover parameter */
    memset(&coverParams, 0, sizeof(coverParams));
    FASTCOVER_convertToCoverParams(parameters, &coverParams);
    /* Checks */
    if (!FASTCOVER_checkParameters(coverParams, dictBufferCapacity, parameters.f, parameters.accel)) {
        DISPLAYLEVEL(1, "FASTCOVER parameters incorrect\n");
        return ERROR(parameter_outOfBound);
    }
    if (nbSamples == 0) {
        DISPLAYLEVEL(1, "FASTCOVER must have at least one input file\n");
        return ERROR(srcSize_wrong);
    }
    if (dictBufferCapacity < ZDICT_DICTSIZE_MIN) {
        DISPLAYLEVEL(1, "dictBufferCapacity must be at least %u\n", ZDICT_DICTSIZE_MIN);
        return ERROR(dstSize_tooSmall);
    }
    /* Assign corresponding FASTCOVER_accel_t to accelParams*/
    accelParams = FASTCOVER_defaultAccelParameters[parameters.accel];
    /* Initialize context */
    {
        size_t const initVal = FASTCOVER_ctx_init(&ctx,
                                                  samplesBuffer,
                                                  samplesSizes,
                                                  nbSamples,
                                                  coverParams.d,
                                                  parameters.splitPoint,
                                                  parameters.f,
                                                  accelParams);
        if (ZSTD_isError(initVal)) {
            DISPLAYLEVEL(1, "Failed to initialize context\n");
            return initVal;
        }
    }
    COVER_warnOnSmallCorpus(dictBufferCapacity, ctx.nbDmers, g_displayLevel);
    /* Build the dictionary */
    DISPLAYLEVEL(2, "Building dictionary\n");
    {
        /* Initialize array to keep track of frequency of dmer within activeSegment */
        U16* segmentFreqs = (U16*)calloc(((U64)1 << parameters.f), sizeof(U16));
        const size_t tail =
            FASTCOVER_buildDictionary(&ctx, ctx.freqs, dictBuffer, dictBufferCapacity, coverParams, segmentFreqs);
        const unsigned nbFinalizeSamples = (unsigned)(ctx.nbTrainSamples * ctx.accelParams.finalize / 100);
        const size_t dictionarySize = ZDICT_finalizeDictionary(dict,
                                                               dictBufferCapacity,
                                                               dict + tail,
                                                               dictBufferCapacity - tail,
                                                               samplesBuffer,
                                                               samplesSizes,
                                                               nbFinalizeSamples,
                                                               coverParams.zParams);
        if (!ZSTD_isError(dictionarySize)) {
            DISPLAYLEVEL(2, "Constructed dictionary of size %u\n", (unsigned)dictionarySize);
        }
        FASTCOVER_ctx_destroy(&ctx);
        free(segmentFreqs);
        return dictionarySize;
    }
}

ZDICTLIB_API size_t ZDICT_optimizeTrainFromBuffer_fastCover(void* dictBuffer,
                                                            size_t dictBufferCapacity,
                                                            const void* samplesBuffer,
                                                            const size_t* samplesSizes,
                                                            unsigned nbSamples,
                                                            ZDICT_fastCover_params_t* parameters) {
    ZDICT_cover_params_t coverParams;
    FASTCOVER_accel_t accelParams;
    /* constants */
    const unsigned nbThreads = parameters->nbThreads;
    const double splitPoint = parameters->splitPoint <= 0.0 ? DEFAULT_SPLITPOINT : parameters->splitPoint;
    const unsigned kMinD = parameters->d == 0 ? 6 : parameters->d;
    const unsigned kMaxD = parameters->d == 0 ? 8 : parameters->d;
    const unsigned kMinK = parameters->k == 0 ? 50 : parameters->k;
    const unsigned kMaxK = parameters->k == 0 ? 2000 : parameters->k;
    const unsigned kSteps = parameters->steps == 0 ? 40 : parameters->steps;
    const unsigned kStepSize = MAX((kMaxK - kMinK) / kSteps, 1);
    const unsigned kIterations = (1 + (kMaxD - kMinD) / 2) * (1 + (kMaxK - kMinK) / kStepSize);
    const unsigned f = parameters->f == 0 ? DEFAULT_F : parameters->f;
    const unsigned accel = parameters->accel == 0 ? DEFAULT_ACCEL : parameters->accel;
    const unsigned shrinkDict = 0;
    /* Local variables */
    const int displayLevel = parameters->zParams.notificationLevel;
    unsigned iteration = 1;
    unsigned d;
    unsigned k;
    COVER_best_t best;
    POOL_ctx* pool = NULL;
    int warned = 0;
    /* Checks */
    if (splitPoint <= 0 || splitPoint > 1) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect splitPoint\n");
        return ERROR(parameter_outOfBound);
    }
    if (accel == 0 || accel > FASTCOVER_MAX_ACCEL) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect accel\n");
        return ERROR(parameter_outOfBound);
    }
    if (kMinK < kMaxD || kMaxK < kMinK) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect k\n");
        return ERROR(parameter_outOfBound);
    }
    if (nbSamples == 0) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "FASTCOVER must have at least one input file\n");
        return ERROR(srcSize_wrong);
    }
    if (dictBufferCapacity < ZDICT_DICTSIZE_MIN) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "dictBufferCapacity must be at least %u\n", ZDICT_DICTSIZE_MIN);
        return ERROR(dstSize_tooSmall);
    }
    if (nbThreads > 1) {
        pool = POOL_create(nbThreads, 1);
        if (!pool) {
            return ERROR(memory_allocation);
        }
    }
    /* Initialization */
    COVER_best_init(&best);
    memset(&coverParams, 0, sizeof(coverParams));
    FASTCOVER_convertToCoverParams(*parameters, &coverParams);
    accelParams = FASTCOVER_defaultAccelParameters[accel];
    /* Turn down global display level to clean up display at level 2 and below */
    g_displayLevel = displayLevel == 0 ? 0 : displayLevel - 1;
    /* Loop through d first because each new value needs a new context */
    LOCALDISPLAYLEVEL(displayLevel, 2, "Trying %u different sets of parameters\n", kIterations);
    for (d = kMinD; d <= kMaxD; d += 2) {
        /* Initialize the context for this value of d */
        FASTCOVER_ctx_t ctx;
        LOCALDISPLAYLEVEL(displayLevel, 3, "d=%u\n", d);
        {
            size_t const initVal =
                FASTCOVER_ctx_init(&ctx, samplesBuffer, samplesSizes, nbSamples, d, splitPoint, f, accelParams);
            if (ZSTD_isError(initVal)) {
                LOCALDISPLAYLEVEL(displayLevel, 1, "Failed to initialize context\n");
                COVER_best_destroy(&best);
                POOL_free(pool);
                return initVal;
            }
        }
        if (!warned) {
            COVER_warnOnSmallCorpus(dictBufferCapacity, ctx.nbDmers, displayLevel);
            warned = 1;
        }
        /* Loop through k reusing the same context */
        for (k = kMinK; k <= kMaxK; k += kStepSize) {
            /* Prepare the arguments */
            FASTCOVER_tryParameters_data_t* data =
                (FASTCOVER_tryParameters_data_t*)malloc(sizeof(FASTCOVER_tryParameters_data_t));
            LOCALDISPLAYLEVEL(displayLevel, 3, "k=%u\n", k);
            if (!data) {
                LOCALDISPLAYLEVEL(displayLevel, 1, "Failed to allocate parameters\n");
                COVER_best_destroy(&best);
                FASTCOVER_ctx_destroy(&ctx);
                POOL_free(pool);
                return ERROR(memory_allocation);
            }
            data->ctx = &ctx;
            data->best = &best;
            data->dictBufferCapacity = dictBufferCapacity;
            data->parameters = coverParams;
            data->parameters.k = k;
            data->parameters.d = d;
            data->parameters.splitPoint = splitPoint;
            data->parameters.steps = kSteps;
            data->parameters.shrinkDict = shrinkDict;
            data->parameters.zParams.notificationLevel = g_displayLevel;
            /* Check the parameters */
            if (!FASTCOVER_checkParameters(data->parameters, dictBufferCapacity, data->ctx->f, accel)) {
                DISPLAYLEVEL(1, "FASTCOVER parameters incorrect\n");
                free(data);
                continue;
            }
            /* Call the function and pass ownership of data to it */
            COVER_best_start(&best);
            if (pool) {
                POOL_add(pool, &FASTCOVER_tryParameters, data);
            } else {
                FASTCOVER_tryParameters(data);
            }
            /* Print status */
            LOCALDISPLAYUPDATE(displayLevel, 2, "\r%u%%       ", (unsigned)((iteration * 100) / kIterations));
            ++iteration;
        }
        COVER_best_wait(&best);
        FASTCOVER_ctx_destroy(&ctx);
    }
    LOCALDISPLAYLEVEL(displayLevel, 2, "\r%79s\r", "");
    /* Fill the output buffer and parameters with output of the best parameters */
    {
        const size_t dictSize = best.dictSize;
        if (ZSTD_isError(best.compressedSize)) {
            const size_t compressedSize = best.compressedSize;
            COVER_best_destroy(&best);
            POOL_free(pool);
            return compressedSize;
        }
        FASTCOVER_convertToFastCoverParams(best.parameters, parameters, f, accel);
        memcpy(dictBuffer, best.dict, dictSize);
        COVER_best_destroy(&best);
        POOL_free(pool);
        return dictSize;
    }
}
